A report Thursday also criticizes the Nigerian government for failing to account for hundreds of men and boys rounded up by security forces using emergency powers in the Islamic uprising. The London-based organization quotes witnesses saying hundreds have died of dehydration, illness and beatings while many other detainees have been executed.

It quotes commanders of vigilante groups describing the rescue of kidnapped women and girls in attacks on hideouts of the Boko Haram terrorist network. Some were pregnant and others had babies.

Human Rights Watch also accused Boko Haram of using children as young as 12 in hostilities.

Boko Haram is blamed for the killings of hundreds of civilians in recent months.